Okay... I've searched all over the Internet and Rock Auto, Autozone, etc. and cannot find a rebuilt or replacement proportioning valve for the 1980 D-50 2WD Sports. Mine is apparently hosed, little application of front brakes, rear applies until lock-up to stop. New master cylinder installed, multiple bleeding of system (almost a gallon of brake fluid used in multiple flushings, etc. until it bled clean and clear with no air.)

Apparently the valve above, which is available, won't work?

So what can I do now to get this truck back on the road with good brakes?

She really needs help!

Thank you.